If you have spent any time around boats, beaches or dive sites, you have seen it: a red flag with a white diagonal stripe, floating on a buoy or flying from a boat. That is the diver down flag, and it is one of the most important signals on the water. Here is what it means, how it differs from the blue and white flag, and what boaters and divers should do when they see one.
The short answer
A diver down flag means there are divers or snorkelers in the water nearby. Boats should slow down to idle or no-wake speed and keep well away. There are two versions: the red flag with a white diagonal stripe, used mainly in the United States and Canada, and the blue and white "Alpha" flag, the international signal flown by a boat that has divers down.
The red and white flag
The red flag with a white stripe running from top left to bottom right is the classic "diver down" flag. In the US and Canada it is the flag recreational divers and snorkelers use, on a boat or on a float that the diver tows or stays close to. It marks the place where people are underwater.
It has become a symbol of diving itself. You see it on dive shop signs, stickers, mugs and dive clothing, because to divers it simply means "this is our world".
The blue and white Alpha flag
The Alpha flag is the letter "A" in the international code of signals: white on the side near the mast, blue on the other side with a swallowtail cut. Flown by a boat, it means "I have a diver down; keep well clear at slow speed." It is a signal about the boat, which cannot move out of the way because its divers are in the water.
In many places outside North America, the Alpha flag is the official diving signal. In the US, many dive boats fly both: the red and white flag for local boaters and the Alpha flag for larger vessels that follow international rules.
Red vs blue at a glance
- Red with white stripe: marks where divers are. Used mostly in the US and Canada. Can be on a boat or a float.
- Blue and white Alpha: marks a boat with divers down that can't maneuver freely. International.
- Both mean the same thing to other boats: slow down and stay away.
How far should boats stay away?
It depends on where you are, because the rules are set by each state or country. Common rules in the US are around 100 feet in rivers, inlets and narrow channels and around 300 feet in open water, and boats that must come closer have to slow to idle speed. Some places use different distances, and a few have no specific rule at all. Always check the local regulations for the area you boat or dive in.
What divers and snorkelers should do
- Fly the flag only while people are in the water. Take it down when everyone is back on board, so the signal keeps its meaning.
- Stay close to it. Many places require divers to stay within a set distance of their flag, often 100 to 300 feet. A flag far from the divers protects no one.
- Use a float or buoy when shore diving or snorkeling, so boaters can see where you are.
- Don't rely on the flag alone. Surface carefully, look and listen for boats, and ascend near your flag or the boat.
What boaters should do
- Slow down as soon as you see a dive flag, and keep a lookout for bubbles and heads in the water.
- Give the flag the distance the local rules require, and pass at idle speed if you must come closer.
- Never drive between a dive boat and its flag or float.
Wear the flag
For many divers the red and white flag is a badge of pride. If you want to wear it, our diver down flag apparel puts it on rash guards, hoodies, polos and hats. Popular picks are the Diver Down Flag rash guard, the Diver Down Shark rash guard and the Diver Flag hoodie. If you are new to dive wear, our guide to the best rash guards for scuba diving explains what to look for.
Quick answers
What does a red flag with a white stripe mean in the water? Divers or snorkelers are below the surface nearby. Slow down and keep clear.
What does the blue and white flag mean? It is the international Alpha flag: the boat has divers down and can't move freely, so keep well clear at slow speed.
Is a dive flag required by law? In many US states and in Canada, yes, when diving in areas open to boats. Rules differ, so check locally.
Is the diver down flag a distress signal? No. It only says people are in the water. It does not mean someone needs help.